Prevalence and Overtesting of True Heparin-Induced Thrombocytopenia in a 591-Bed Tertiary Care, Teaching Hospital

Abstract

Heparin-induced thrombocytopenia type II (HIT) is a rare but potentially fatal antibody-mediated reaction to all forms of heparin (unfractionated heparin, low-molecular weight heparin, heparin flushes, and heparin-coated catheters), which can lead to HIT with thrombosis. Two tests commonly used to screen for HIT include the enzyme-linked immunosorbent assay (ELISA) and serotonin release assay (SRA). This is a retrospective chart review study conducted from January 1, 2013, through December 31, 2014, to estimate the rate of true HIT in critical care patients at Winthrop-University Hospital, located in Mineola, New York. Patients are classified as positive for HIT if both ELISA and SRA immunoassays are positive. We reviewed 507 heparin immunoassays, excluding 64 who had an inappropriate ELISA test sent due to no administration of heparin, enoxaparin, or heparin lock flush at this or previous hospital stays at Winthrop. Of the 443 heparin immunoassays, ELISA results were positive for 66 patients (15.1%), and only 11 (2.5%) patients had true cases of HIT with a 95% confidence interval of 1.3% to 4.4%. The 4T score for those with true HIT (median: 5.0) was statistically higher compared to those without true HIT (median: 2.0; P < .001). Despite guidelines in place, overtesting for HIT is still a prevalent issue.